Hello John Truong,
It is possible. It may require a bit more work to get it working in all situations, but it should be possible.
In order to place a handle, you can template the nodes. Then you should mark the handle somehow, e.g. with a css class.
Then on ClientNodeDragStart you will have to check the element on which the event occurred. For this purpose you can use the dom event in the arguments. If the click happened outside the element with the css class, you can cancel the dragging. Here is a reference to for this event: http://www.telerik.com/help/aspnet-ajax/tree_clientonclientnodedragstart.html
I hope this is helpful for you!
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